Pens of the type described by way of introduction can be used for, inter alia, electronic recording of handwritten information, as is known from e.g. U.S. Pat. No. 5,652,412, WO 00/25293, U.S. Pat. No. 5,294,792, U.S. Pat. No. 5,852,434 and WO 00/73983. Here a sensor records, preferably via one or more imaging components, images of an area around or beside the contact point of the writing means on a base. Each of the images may comprise, for example, part of a pattern applied to the base and/or part of the pen strokes made with the aid of the writing means on the base. An image processor, in the pen or in an external unit, receives the images from the sensor and creates, based on these, an electronic copy of the information handwritten on the base, in the form of a sequence of mutually related positions.
However, it may be difficult to manufacture the above prior-art pens in large volumes owing to the long tolerance chains that exist between the components included which convert a physical pen stroke on a writing base into a sequence of positions. If the tolerance of each individual component is not kept at a minimum, which is costly, the relative positioning of the components will thus vary quite significantly between different items of pens. As a result, many pens must be rejected in manufacture in that some items have insufficient precision in the recording of handwritten information.
The above prior-art pens are besides sensitive to mechanical shocks since there is a risk that the components inside the pen are displaced relative to each other if, for instance, the pen is dropped onto the floor.
Corresponding disadvantages appear in the electronic pen which is disclosed in WO 01/22208. The pen has an ink cartridge which extends into the interior of the pen for cooperation with a sensor which detects when the pen is contacted with a base. The ink cartridge is controlled by means of a threaded metal cone which is screwed to the casing at the front end of the pen, in the same way as in ordinary ball point pens. The pen also has an image sensor which is fixed to a printed circuit board in the pen, and an imaging system which is placed within the front end of the pen. Variations in the thread of the metal cone and in the screwing to the casing may result in the position of the ink cartridge in the pen varying between different items of pens. The position of the image sensor on the printed circuit board and the location of the printed circuit board in the interior of the pen may also vary between different items, as may also the location of the imaging system. Summing up, also this type of pen has long tolerance chains which may have a detrimental effect on the yield in serial production thereof.
Prior-art technique also includes U.S. Pat. No. 5,774,602 and WO 01/30589.